Drilling fluids used in the drilling of subterranean oil and gas wells along with other drilling fluid applications and drilling procedures are well known. In rotary drilling there are a variety of functions and characteristics that are expected of drilling fluids, also known as drilling muds, or simply “muds”.
Drilling fluids are typically classified according to their base fluid. In water-based muds, solid particles are suspended in water or brine. Oil can be emulsified in the water which is the continuous phase. Brine-based drilling fluids, of course are a water-based fluid (WBF) in which the aqueous component is brine. These may also be called water-based muds (WBMs). Oil-based fluids (OBFs) are the opposite or inverse. Solid particles are often suspended in oil, and water or brine is emulsified in the oil and therefore the oil is the continuous phase. Oil-based muds (OBMs) can be either all-oil based or water-in-oil macroemulsions, which are also called invert emulsions. In oil-based mud the oil can consist of any suitable oil that may include, but is not limited to, diesel, mineral oil, synthetic oil, esters, or olefins. OBFs as defined herein also include synthetic-based fluids or muds (SBFs or SBMs) which are synthetically produced rather than refined from naturally-occurring materials. SBFs often include, but are not necessarily limited to, olefin oligomers of ethylene, esters made from vegetable fatty acids and alcohols, ethers and polyethers made from alcohols and polyalcohols, paraffinic, or aromatic hydrocarbons, alkyl benzenes, terpenes and other natural products and mixtures of these types.
Inventory management of contaminated O/SBF is one of the biggest challenges in the oil and gas industry. When invert-emulsion drilling fluids are used during a drilling operation, they accumulate contaminants such as drill solids (up to about 20 vol %) and in some instances they also collect formation water. These contaminants have drastic effect on the properties of the drilling fluids. The most common method to reduce the effect of contaminants is to dilute the drilling fluid with base oil. However, this is not the ideal solution since it continues to increase the inventory. It should be understood that the term “contaminated O/SBF” includes, but is not necessarily limited to used OBFs and/or SBFs that has been used at least once as a drilling fluid, completion fluid, workover fluid, stimulation fluid, production fluid or some other oilfield or non-oilfield use, such as a metal cutting fluid.
It would be desirable if the base oil from contaminated O/SBF containing cuttings, drill solids, formation water and formation fluids could be recovered and reused in order to minimize growing the inventory.